U.S. patent number 5,192,910 [Application Number 07/715,107] was granted by the patent office on 1993-03-09 for temperature-control device for samples.
This patent grant is currently assigned to Spectrospin AG. Invention is credited to Phillip Hepp, Martin Rindlisbacher, Oskar Schett, Werner H. Tschopp.
United States Patent |
5,192,910 |
Hepp , et al. |
March 9, 1993 |
Temperature-control device for samples
Abstract
In a temperature-control device for samples, in particular for
NMR spectroscopy, comprising a vessel (20) provided with an opening
(19) for receiving a measuring sample (1), an inlet opening (10)
for introduction of the fluid, an outlet opening (15) for the
outflow of the fluid and a flow channel (18) through which at least
a partial flow of the fluid is guided past the sample (1), as
direct fluid flow, from the bottom to the top, there is provided at
least one by-pass channel (17) which is arranged in such a way that
an additional partial fluid flow can be guided past the upper area
of the said sample (1) in the form of a by-pass fluid flow (7).
This enables also the upper area of the sample (1) to be
temperature-controlled in an efficient way so as to minimize the
temperature gradient in the sample (1). The temperature-control
device may comprise, in the upper area of the sample (1), a
heat-exchanger system (14) which concentrates the direct fluid flow
( 8), after it has been combined with the by-pass fluid flow (8),
around the sample (1). One achieves in this manner efficient
temperature control of the upper section of the sample by the fluid
flow, without any disturbing thermal obstacles.
Inventors: |
Hepp; Phillip (Binningen,
CH), Tschopp; Werner H. (Aesch/Forch, CH),
Rindlisbacher; Martin (Zurich, CH), Schett; Oskar
(Uster, CH) |
Assignee: |
Spectrospin AG
(CH)
|
Family
ID: |
6408232 |
Appl.
No.: |
07/715,107 |
Filed: |
June 10, 1991 |
Foreign Application Priority Data
|
|
|
|
|
Jun 12, 1990 [DE] |
|
|
4018734 |
|
Current U.S.
Class: |
324/315;
324/318 |
Current CPC
Class: |
B01L
7/00 (20130101); G01R 33/307 (20130101); G01R
33/31 (20130101) |
Current International
Class: |
B01L
7/00 (20060101); G01R 33/31 (20060101); G01R
33/30 (20060101); G01V 003/00 () |
Field of
Search: |
;324/300,307,309,315,318,321 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
0175789 |
|
Feb 1985 |
|
EP |
|
3027891 |
|
Feb 1981 |
|
DE |
|
1-299448 |
|
Dec 1989 |
|
JP |
|
1196820 |
|
Jul 1970 |
|
GB |
|
85/04020 |
|
Sep 1985 |
|
WO |
|
Other References
J Phys. E: Sci. Instrum., vol. 12, 1979, P. Bruesch and W.
Foditsch, "A versatile high- and low-temperature optical cell for
reflectivity, transmission and light-scattering experiements", pp.
872 to 874. .
Yoshida "Modified Variable Temperature Control Unit for NMR
Spectrometers" Rev Sci Instr Bd52 Nr3 Mar. 1981. .
Aguilar-Parrilla et al. "Temp. Gradients & Sample Heating in
Variable Temp. High Speed Mas NMP Sgec." Jo. Mag. Res. Bd187 Nr3
May 1990..
|
Primary Examiner: Arana; Louis
Attorney, Agent or Firm: Hackler; Walter A.
Claims
What is claimed is:
1. Temperature-control device for NMR spectroscopy, comprising:
a vessel provided with an opening for receiving a measuring sample,
at least one inlet opening for introduction of a temperature
controlling fluid into the vessel, and one outlet opening for
outflow of the temperature controlling fluid from the vessel;
flow channel means for separating the temperature controlling fluid
into partial flows upon entry into the vessel and for guiding one
partial flow of the temperature controlling fluid past the sample
as direct fluid flow, from a bottom to a top of the sample; and
at least one by-pass channel means for guiding another of the
partial fluid flows past an upper area of the sample in the form of
a by-pass fluid flow.
2. Temperature-control device according to claim 1, wherein a
temperature sensor is provided in a lower area of the sample, in
the direct fluid flow.
3. Temperature-control device according to claim 2, wherein an
additional temperature sensor is provided in the upper area of the
sample, in the by-pass fluid flow.
4. Temperature-control device according to claim 1, further
comprising means for detecting a lineshape of an NMR signal from
the sample and indicating the temperature of the sample at an axial
position, based on the line width of the NMR signal.
5. Temperature-control device for NMR spectroscopy comprising:
a vessel provided with an opening for receiving a measuring sample,
two separate inlet openings for introduction of temperature
controlling fluids into the vessel and an outlet opening for
outflow of the temperature controlling fluids from the vessel;
flow channel means for guiding one temperature controlling fluid
past the sample as direct fluid flow, from a bottom to a top of the
sample;
by-pass channel means for guiding another temperature controlling
fluid past an upper area of the sample in the form of a by-pass
fluid flow; and
separate supply lines for connection to the two separate inlet
openings to provide the direct fluid flow and the by-pass fluid
flow.
6. Temperature-control device according to claim 5, further
comprising means for separately controlling the temperature of the
direct flow and the by-pass fluid flow.
7. Temperature-control device according to claim 1, further
comprising valve means for controlling at least one of the direct
fluid flow through the flow channel and the by-pass fluid flow
through the by-pass channel.
8. Temperature-control device according to claim 7, further
comprising control means for controlling flow rates of the partial
flows through the said flow channel and the by-pass channel in such
a way that a presettable controlled variable can be kept
constant.
9. Temperature-control device according to claim 7, further
comprising control, means for controlling temperatures of the
partial flows through the said flow channel and the by-pass channel
in such a way that a presettable controlled variable can be kept
constant.
10. Temperature-control device according to claim 1 further
comprising heat-exchanger means disposed in the upper area of the
sample for concentrating the direct fluid flow around the sample,
after it has been united with the by-pass fluid flow.
11. Temperature-control device according to claim 10, wherein the
heat-exchanger means includes a conduit tube enclosing the upper
area of the sample over an axial length of exchange, at a small
radial spacing, said heat exchanger means further comprising in a
lower area thereof, baffle means for deflecting the by-pass fluid
flow in a direction toward the sample.
12. Temperature-control device according to claim 10, wherein the
heat-exchanger means has a length selected to minimize heat loss
from the temperature controlling fluid to the heat-exchanger means,
and a small mass, thermal capacity and thermal conductivity
relative to the mass, thermal capacity and thermal conductivity of
the sample.
13. Temperature-control device according to claim 11, wherein the
heat-exchanger means comprises, on an inner surface facing the said
sample, a spiral groove extending axially over the axial length of
exchange.
14. Temperature-control device according to claim 8, wherein the
presettable controlled variable is one of the following variables:
the temperature in the lower area of the sample; the temperature in
the upper area of the said sample; the temperature difference
between the upper and the lower areas of the aid sample; a total
fluid flow .phi.; the partial flow rate of the direct fluid flow;
the partial flow rate of the by-pass fluid flow; and a product of
at least two of the variables.
15. Temperature-control device according to claim 9, wherein the
presettable controlled variable is one of the following variables:
the temperature in the lower area of the sample; the temperature in
the upper area of the sample; the temperature difference between
the upper and the lower areas of the sample; a total fluid flow
.phi.; the partial flow rate of the direct fluid flow; the partial
flow rate of the by-pass fluid flow; and a product of at least two
of the variables.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a temperature-control device for
samples, in particular for NMR spectroscopy, comprising a vessel
provided with an opening for receiving a measuring sample, an inlet
opening for introduction of a fluid, an outlet opening for the
outflow of the fluid and a flow channel through which at least a
partial flow of the fluid is guided past the sample, as direct
fluid flow, from the bottom to the top.
A device of this type has been known, for example, from EP-A2-0 175
789.
In examining samples, for example by NMR spectroscopy, but also by
optical spectroscopy or infrared spectroscopy, it is frequently
required that certain sample substances be measured at different
temperatures. During such measurements at different temperatures,
the spectra normally vary due to the fact that, on the one hand,
the heights and widths and, on the other hand, the resonance
frequencies of the spectral lines may be temperature-dependent.
If this temperature-dependence of the spectra is to be determined
exactly, it is necessary that a constant temperature distribution
be attained over the whole active sample volume. Otherwise,
adulterations of the desired effect may occur insofar as different
volume elements within the sample exhibit different temperatures
and may, consequently, in particular in NMR spectroscopy, produce
various lines with displaced resonance points which may superpose
and may, thus, lead to distorted lineshapes.
The operation of the known temperature-control devices, above all
of those used in NMR spectroscopy but also of those used in optical
and infrared spectroscopy, is generally such that a cooled or
heated fluid, preferably nitrogen gas, is caused to flow past the
surface of a cylindrical sample, from the bottom to the top, in
order to bring the sample to the desired temperature.
In order to improve the spectral resolution, it is necessary in
most of the cases to rotate the sample. This is effected by placing
the upper area of the test tube, which contains the sample
material, in the rotor of an air turbine which ensures on the one
hand that the test tube is positioned correctly, and on the other
hand, that it can be rotated.
However, this way of holding the sample firstly results in the
situation that the upper area of the test tube cannot be sealed
hermetically and that, consequently, the lower part, which can be
sealed hermetically, is preferred for introducing the fluid. This
means that, preferably, the fluid flow is guided past the test tube
from the bottom to the top.
On the other hand, this way of holding the sample has the
consequence that if the sample is heated, its bottom area will be
heated to a higher temperature than its upper area as a certain
amount of heat is dissipated via the point of contact between the
test tube and the air turbine. It is this point of contact which
plays an important part in the development of an axial temperature
gradient in the test tube. In order to counteract the development
of this temperature gradient, it would be desirable to have the
fluid flow along the test tube from the top to the bottom; but this
is connected with technical difficulties, as has been explained
above.
In the case of another known arrangement, improved temperature
homogeneity is achieved inside the sample by the fact that the
temperature-controlling fluid is guided to the bottom of the sample
by sort of a countercurrent process. The fluid flows in this case
initially from the top to the bottom along the walls of a glass
tube which accommodates the test tube containing the sample. The
glass tube is open at its bottom so that the fluid is permitted to
enter the space between the glass tube and the sample at this point
from the bottom to the top and to flow thereafter along the sample
from the bottom to the top, in direct contact with the test tube.
If the fluid is to heat up the sample, for example, the glass tube
will be heated up in this case to a higher temperature at the top
than at the bottom so that, due to the radial heat transmission
toward the sample, it contributes towards reducing the temperature
drop encountered in the test tube in the direction from the bottom
to the top. This effect, which counteracts the temperature gradient
is, however, very limited because on the one hand the relatively
big mass of the test tube, filled with the sample substance,
requires correspondingly important heat quantities in order to
change its temperature, and because on the other hand it is very
difficult to transmit this relatively important heat quantity in
radial direction, the wall thickness of the glass tube as well as
the fluid flow between the test tube and the glass tube acting as
thermal obstacles. In addition, the countercurrent principle is
connected with the further drawback that the fluid flow changes its
direction several times, which produces an increased flow
resistance and, consequently, higher pressures for a given total
flow volume .phi. of the fluid.
The conventional temperature-control device for samples illustrated
in FIG. 1 shows a standard arrangement of the type used mainly in
NMR spectroscopy. A sample 1 has been introduced into a vessel 20
with an outer heat insulation 3 (consisting, for example, of glass
wool, expanded plastic, a vacuum, etc.), through an opening 19. A
cylindrical carrier tube 6, which encloses the sample 1, carries a
first RF coil 13, normally a NMR receiver coil, so that the sample
is embraced by the latter. A second cylindrical carrier tube 5
comprising a second RF coil 12, for example a NMR decoupling coil,
surrounds the first carrier tube 6 at a radial distance. A third
wall 4, for example a cylindrical glass tube, surrounds the second
carrier tube 5 at a radial distance and serves as additional
thermal insulation for the arrangement.
An inlet opening 10 admits a direct fluid flow 8, normally a gas
flow, which is guided against the sample 1 from below and which
then enters the flow channel 18 between the sample 1 and the first
carrier tube 6, leaving it again at the upper end of the sample 1
through the outlet opening 15.
By feeding the temperature-controlling fluid directly to the test
tube, it is possible to attain the desired sample temperature very
quickly and with a relatively small fluid flow rate. A serious
disadvantage of this arrangement lies, however, in the poor axial
homogeneity of the temperature in the sample, because when the
sample is to be heated the test tube will get much warmer at the
bottom than at the top, and when the sample is to be cooled, it
will get much cooler at the bottom than at the top. This situation
could of course be improved to some extent by increasing the fluid
flow rate. However, since for metrological reasons the spacing
between the sample 1 and the first carrier tube 6 must be kept as
small as possible in order not to impair unnecessarily the
signal-to-noise ratio, any increase of the fluid flow rate would
lead to higher pressures in the lower area of the sample 1 and,
consequently, to an inadmissible axial displacement of the test
tube in upward direction.
Improved temperature homogeneity in the sample 1 is achieved by the
known arrangement illustrated in FIG. 2, which operates according
to the countercurrent principle. In this case, the
temperature-controlling fluid is admitted to the vessel 20 through
the inlet opening 10, flows through the space between the wall 4
and the second carrier tube 5 from the bottom to the top, is then
deflected, by the upper cover of the vessel 20, in downward
direction and into the space between the first carrier tube 6 and
the second carrier tube 5, passes this space from the top to the
bottom, and is then once more deflected by the lower cover of the
vessel 20 in upward direction and into the flow channel 18 between
the sample 1 and the first carrier tube 6. The flow channel 18 is
passed by the direct fluid flow from the bottom to the top,
whereafter the flow leaves the vessel 20 through the outlet opening
15.
Since in the case of this arrangement, when the sample 1 is to be
heated, the direct fluid flow 8, which up to this point has
dissipated practically no heat to the environment, heats up the
carrier tube 6 directly neighboring the test tube more strongly in
its upper area than in its lower area, the axial temperature drop
necessarily occurring in the test tube in the case of the
arrangement of FIG. 1 can be reduced to some extent by radial heat
transmission from the first carrier tube 6 to the upper area of the
sample 1. Given the fact, however, that the sample 1 has a much
greater heat capacity and thermal conductivity than the other parts
of the arrangement passed by the direct fluid flow 8 and that,
consequently, a relatively greater amount of heat is required if
the temperature gradient in the sample 1 is to be influenced
notably, the radial heat transmission from the upper area of the
first carrier tube 6 to the upper area of the sample 1 is by far
not sufficient to attain axial homogeneity of the temperature in
the sample, at least approximately. It is especially the wall
thickness of the first carrier tube 6 and the direct fluid flow 8
passing between the first carrier tube 6 and the surface of the
test tube which prevents any notable heat transmission. In
addition, the direct fluid flow 8 is deflected several times in the
case of the arrangement according to FIG. 2, and this results in a
higher flow resistance which in turn leads to higher pressures for
a given total flow volume .phi. of the fluid, a condition which is
undesirable as well.
SUMMARY OF THE INVENTION
Starting out from the state of the art, it is the object of the
present invention to provide a temperature-control device of the
type described above which is capable of achieving a homogeneous
temperature curve inside the sample and of reaching the state of
thermal equilibrium in the sample within the shortest possible
time.
The invention achieves this object by the fact that at least one
by-pass channel is provided which is arranged in such a way that an
additional partial fluid flow can be guided past the upper area of
the sample in the form of a by-pass fluid flow.
With the aid of the by-pass fluid flow, it is rendered possible to
heat or cool efficiently especially the upper part of the sample,
whereby the temperature gradient inside the sample is reduced. The
fact that the by-pass fluid flow is guided along the upper area of
the sample directly and without any thermal obstacle enables the
desired stable temperature curve to build up quickly inside the
sample, the time required until the state of thermal equilibrium is
reached being only dependent on the thermal properties of the
sample.
According to one embodiment of the invention, a temperature sensor
is provided in the lower area of the sample, in the direct fluid
flow. This temperature sensor serves for picking up the actual
value of the sample temperature, or the temperature of the fluid
flowing past the sample at this point.
An additional temperature sensor may be provided in the upper area
of the sample, in the by-pass fluid flow, in order to be able to
measure the temperature also at this point.
Another embodiment of the invention comprises a device which is
capable of detecting the lineshape of the NMR signal from the
sample and of indicating the temperature of the sample at an axial
position, based on the line width of the NMR signal. This indirect
temperature measurement allows on the one hand to do without the
temperature sensors, and ensures on the other hand that one
actually measures the temperature which is really relevant, namely
the temperature of the sample, and not the latter's environmental
temperature.
According to a preferred embodiment of the invention, separate
supply lines are provided for the direct fluid flow and the by-pass
fluid flow to the vessel. This leads to the positive result that
the two partial fluid flows are united only in the upper area of
the sample. According to a further improvement of this embodiment
of the invention, there are provided in addition separate heating
and/or cooling means for controlling the temperature of the direct
flow and of the by-pass fluid flow, respectively. It is thus
possible to supply the two partial fluid flows to the vessel at
different temperature levels so as to compensate for the increased
heat exchange between the by-pass fluid flow and the wall of the
by-pass channel relative to the extremely low heat exchange between
the direct sample flow and its environment, from the point of its
entry into the vessel up to the point where it gets into contact
with the sample.
According to a preferred embodiment of the invention, there is
provided at least one valve for controlling the flow rate of the
direct fluid flow through the flow channel and/or the flow rate of
the by-pass fluid flow through the by-pass channel. Such a valve
also enables the partial fluid flows to be adjusted in such a way
that different requirements can be met for different measurements.
By selecting the valve orifice in a suitable manner it is possible,
for example, to adjust the two partial fluid flows for a given
total flow .phi. in such a way that the smallest possible
temperature gradient is obtained over the axial length of the
sample, without substantial reduction of the maximum temperature
that can be achieved at the sample.
According to a particularly preferred embodiment of the
temperature-control device for samples proposed by the invention,
there is provided a control device which controls the partial fluid
flows through the flow channel and the by-pass channel in such a
way that a presettable controlled variable can be kept constant.
This control device enables different presettable operating
parameters for the measurement to be controlled automatically.
The presettable controlled variable may be the temperature in the
lower or upper area of the sample, the temperature difference
between the upper and the lower areas of the sample, the total
fluid flow .phi., the partial flow rate of the direct fluid flow,
the partial flow rate of the by-pass fluid flow, or a product of a
plurality of these parameters. It is thus possible, for example by
controlling the absolute temperature of the sample, to achieve in
the sample a stable temperature curve over time. A particularly
advantageous solution is obtained when the temperature difference
between the upper and the lower areas of the sample is controlled
to a minimum. Further, it is also possible to control the fluid
flows in such a way that the state of thermal equilibrium is
obtained in the sample within the shortest possible time and with a
constant flow rate of the fluid.
According to a particularly preferred embodiment of the
temperature-control device for samples proposed by the invention, a
heat-exchanger system is provided in the upper area of the sample,
which system concentrates the direct fluid flow around the sample,
after it has been united with the by-pass fluid flow. One achieves
in this manner for the upper sample section an effective
temperature control by the united fluid flow, without any
disturbing thermal obstacles. The heat-exchanger system may display
the form of a conduit tube which encloses the upper area of the
sample over an axial length of exchange, at a small radial spacing,
and which comprises in its lower area one or more baffles which act
to deflect the by-pass fluid flow in a direction toward the sample.
This brings the fluid flow into intimate contact with the upper
area of the sample and ensures in this manner efficient direct
cooling or heating of the sample along the axial length of
exchange.
According to an advantageous further improvement, the
heat-exchanger system has a big axial length of exchange, relative
to the axial length of the sample, and small mass, thermal capacity
and thermal conductivity relative to the mass, thermal capacity and
thermal conductivity of the sample. This keeps the heat losses of
the fluid flow caused by the heat dissipation to the heat-exchanger
system at a low level and the state of thermal equilibrium of the
sample, at the desired temperature, is reached within a
particularly short time and with the least possible flow rate.
According to a particularly preferred further improvement of the
temperature-control device for samples proposed by the invention,
the heat-exchanger system comprises on its surface facing the
sample a spiral groove extending axially over the axial length of
exchange. This forces the fluid flowing through the space between
the heat-exchanger system and the sample to flow around the test
tube along a spiral path, whereby the effective axial length of
exchange is considerably increased and the time available for the
heat exchange between the fluid and the sample is considerably
extended. This effect is particularly valuable in the case of
non-rotating samples.
The invention will now be described and explained in more detail by
way of the example illustrated in the drawing. It is understood
that the features that can be derived from the specification and
the drawing may be employed in other embodiments of the invention
individually or in any combination.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an axial section through a prior art temperature
control device for samples.
FIG. 2 shows an axial section through a prior art temperature
control device for samples, operating according to the counter
current principle.
FIG. 3 shows an axial section through a temperature-control device
for samples according to the invention;
FIG. 4a shows the recorded temperature curves over time for a
sample, for the cases of direct temperature control, temperature
control using the temperature-control device for samples according
to the present invention, and temperature control using a
conventional temperature-control device for samples operating
according to the countercurrent principle;
FIG. 4b shows the axial temperature difference in the sample as a
function of the total fluid flow, for rotating and non-rotating
samples and for the cases of temperature control according to the
invention and conventional temperature control according to the
countercurrent principle; and
FIG. 5 shows an axial section through a temperature-control device
for samples according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 3 illustrates one embodiment of the temperature-control device
for samples proposed by the invention which is suited in particular
for use in NMR spectroscopy, but also in optical or infrared
spectroscopy, for example. The temperature-controlling fluid is
introduced through an inlet opening 10 into the vessel 20 where it
is divided into two partial fluid flows, namely the direct fluid
flow 8, and the by-pass fluid flow 7. The direct fluid flow 8
passes the flow channel 18 between the first carrier tube 6 and the
sample 1 from the bottom to the top, just as in the case of the
conventional devices, cooling or heating thereby the sample 1,
which process gives rise to an axial temperature gradient in the
sample, just as in the case of the known devices.
In order to counteract this temperature gradient, the by-pass fluid
flow 7, which is guided through one or more by-pass channels 17, in
parallel to the direct fluid flow 8, is deflected in the upper area
of the arrangement by a baffle 16 --which may be part of a
heat-exchanger system 14--toward the upper area of the sample.
Given the fact that there are no masses of high thermal capacity at
the boundary surfaces of the by-pass channel 17, the by-pass fluid
flow 7 still has substantially the same temperature at the point
where it contacts the sample 1 which it had at the point of
division from the total fluid flow. In case the sample 1 is to be
heated, the mixing temperature of the combined fluid flow is much
higher at the junction point of the fluid flows in the upper area
of the sample 1 than the temperature of the direct fluid flow 8 at
that same point, the fluid flow 8 having already dissipated a
considerable amount of heat to the sample 1 on its way through the
flow channel 18. The flow ratios of the direct fluid flow 8 and the
by-pass fluid flow 7, and also the total fluid flow .phi. can be
influenced by means of a valve 11 which, in the illustrated
example, is arranged a short way downstream of the inlet opening
10. In order to achieve a situation where the mixing temperature in
the junction area of the two partial fluid flows in the upper area
of the sample is as close as possible to the temperature of the
fluid entering the vessel 20, it is of advantage if a
correspondingly higher flow rate is selected for the by-pass fluid
flow 7 than for the direct fluid flow 8.
If the sample 1 is to be cooled, the fluid flow will normally
consist of a gas flow produced by vaporizing a liquified cryogenic
gas, for example liquid nitrogen or liquid helium, in which case
the pressure required for producing a gas flow is built up
simultaneously. For heating the sample, the gas flow may be taken
directly from a pressure vessel (for example a gas cylinder) and
does not have to be produced first by vaporizing the liquid gas.
The gas flow is brought into contact with an electrically heated
heating coil which brings the gas flow to the desired temperature
by means of an electric control system. Thereafter, the gas flow is
fed to the vessel 20 and to the sample 1 via a thermally insulated
supply line.
In the illustrated example, one can see in the lower area of the
sample 1 a temperature sensor 9 which is in contact with the direct
fluid flow 8 and which transmits to the electric temperature
control device the actual temperature value of the direct fluid
flow 8, which at this point corresponds substantially to the
temperature of the total fluid flow entering the inlet opening 10.
The temperature-control device then compares the actual value with
the entered setpoint value and determines from this comparison the
current required for the heating coil.
In addition to the temperature sensor 9 illustrated in FIG. 3,
there may be provided another temperature sensor--9' --in the
by-pass fluid flow 7 in the upper area of the sample 1, for
measuring the temperature also at this point. This permits in
particular to measure the temperature difference between the upper
and the lower areas of the sample 1, which is a measure of the
temperature gradient prevailing in the sample 1.
Instead of measuring the temperature directly by temperature
sensors, it is also possible to derive the sample temperature at
any axial position indirectly from the lineshape of an NMR signal
from the sample as represented in FIG. 5 by a lineshape shape
detector 100. This is so because an increased temperature gradient
leads to a correspondingly greater line width which may be taken as
a measure of temperature. This provides the possibility to derive
the relevant temperature from the measuring signal proper, for
transmission to the control devices.
Instead of feeding the total fluid flow to the inlet opening 10, as
described before, it is also possible, according to an embodiment
shown in FIG. 5, to feed the partial fluid flows, i.e. the direct
fluid flow 8 and the by-pass fluid flow 7, to the vessel
separately, and to combine the two partial fluid flows only in the
upper area of the sample 1. This provides the particular advantage
that the partial fluid flows may enter the vessel 20 at different
temperature levels. If, for example, the sample 1 is to be heated
up relative to the environmental temperature, the conditions will
be such that, when the total fluid flow is fed into the inlet
opening 10, as illustrated in FIG. 3, the temperature of the
by-pass fluid flow 7 will be lower at the point of combination with
the direct fluid flow 8 in the upper area of the sample 1 than the
temperature of the direct fluid flow 8 at the point where it
impinges upon the lower area of the sample, because on its long way
through the by-pass fluid channel 17 the by-pass fluid flow has
dissipated considerably more heat to the surrounding walls than the
direct fluid flow 8 on its short way from the inlet opening 10 to
the sample. If the two partial fluid flows were given approximately
equal volumes, the upper area of the sample 1 would, therefore,
always have a lower temperature than the lower area, a condition
which could be remedied only by sharply restricting the direct
fluid flow 8, or by increasing substantially the partial flow
volume of the by-pass fluid flow 7. If, however, the two partial
fluid flows can be supplied into the system at different
temperature levels, then the by-pass fluid flow 7 simply can be
given a correspondingly higher temperature level than the direct
fluid flow 8 so as to compensate for the temperature loss of the
by-pass fluid flow 7 on its way through the by-pass channel 17. In
addition, the temperature control device can be designed in such a
way as to enable the temperatures of the two partial fluid flows to
be controlled separately.
For other applications of the invention, the vessel 20 may also be
a cryostat in which case the outer thermal insulation 3 is a dewar
wall and the adjacent inner wall 4 may be designed as an additional
thermal insulation, for example in the form of a radiation shield.
The temperature-controlling fluids may consist in this case of
cryogenic gases, such a nitrogen or helium, which in the case of
low-temperature applications may also flow through the cryostat in
their liquid state.
Further, there may be provided a control device for controlling,
via the valve 11, the partial flows through the flow channel 18 and
the by-pass channel 17 in such a way that a presettable controlled
variable, for example the temperature in the lower and the upper
areas of the sample, the temperature difference between the upper
and the lower areas, the total flow .phi. of the fluid, the partial
flow volumes of the direct fluid flow 8 or of the by-pass fluid
flow 7, or a product of a plurality of these parameters, is kept
constant. For controlling the fluid flow, this control device may
in particular be connected to the before-mentioned electric control
means for the temperature of the gas flow.
The heat-exchanger system 14 provided in the upper area of the
sample 1 serves the purpose to concentrate the direct fluid flow 8,
after it has been combined with the by-pass fluid flow 7, around
the sample 1. In the illustrated embodiment, the heat-exchanger
system 14 has the shape of a conduit tube enclosing the upper area
of the sample 1 over an axial length of exchange 2, at a small
radial spacing. In the lower area of the heat-exchanger system 14,
one can see an inclined baffle surface 16 which deflects the
upwardly flowing by-pass fluid flow 7 toward the sample 1 and which
forces it together with the direct fluid flow 7 into the narrow gap
between the sample 1 and the upper part of the heat-exchanger
system 14. In order to achieve the best possible heat exchange
between the combined fluid flow and the sample 1, the length of the
tubular upper section of the heat-exchanger system 14 and, thus,
the axial length of exchange 2, is chosen as great as possible
relative to the axial length of the sample 1. In order to keep the
thermal losses of the fluid flow, due to heat dissipation to the
heat-exchanger system 14, as small as possible and to reach the
state of thermal equilibrium in the sample 1 at the desired
temperature in the shortest possible time and with the least
possible flow volume of the fluid, the mass, thermal capacity and
thermal conductivity of the heatexchanger system 14 should,
conveniently, be small relative to the sample 1. Especially in the
case of non-rotating samples it is in addition of advantage if the
heat-exchanger system 14 comprises a spiral groove 50 on its
surface facing the sample 1, which is illustrated in FIG. 5 as a
cylindrical surface and which extends in axial direction over the
axial length of exchange 2. This increases the effective axial
length of exchange, or the time available for the heat exchange
between the combined fluid flow and the sample 1 once more quite
considerably.
FIG. 4 shows the measured properties of the temperature-control
device for samples proposed by the invention, by comparison with a
conventional temperature-control device operating according to the
countercurrent principle, or by comparison with the case of direct
temperature control of the sample 1. FIG. 4a shows the recorded
heating curve of the sample 1, as a function of time, for the cases
of direct temperature control (41), temperature control by means of
the temperature-control device for samples (21) according to the
invention and temperature control using a conventional
temperature-control device for samples operating according to the
countercurrent principle (31). It will be readily appreciated that
in the case of the temperature control device for samples according
to the invention the state of thermal equilibrium of the sample 1
is reached almost as quickly as in the case of the direct
temperature control method and that for a given heating capacity
and a given fluid flow .phi., the final temperature reached with
the aid of the temperature-control device for samples according to
the invention is only insignificantly lower. In contrast, the final
temperature reached with the aid of the temperature-control device
for samples operating according to the countercurrent principle is
notably lower and is reached later as well. For the purposes of the
measurements illustrated in FIG. 4a, the temperature curve over
time developing in the sample 1 after connection of a heating
capacity of 20 W was recorded for a constant gas flow .phi.=700
liters/h on a sample 1 having a diameter of 5 mm. FIG. 4b shows the
axial temperature difference in the active area of the same 5 mm
sample which was used also for the measurements illustrated in FIG.
4a, as a function of the total flow quantity .phi. of the gas
flowing at any time through the temperature-control device. The
mean temperature of the sample 1 was in any case equal to 348 K.
The curve 22 was recorded for a temperature-control device for
samples according to the invention with a rotating sample 1, the
curve 23 for the same device with a non-rotating sample 1, while
the curve 32 was recorded for a conventional temperature-control
device for samples operating according to the countercurrent
principle and with a rotating sample, and the curve 33 for the same
conventional device with a non-rotating sample. The temperature
homogeneity inside the sample 1 that can be achieved if the
temperature is controlled using the device according to the
invention is by far superior to that achieved when the temperature
is controlled by means of the conventional device. Especially in
the case of rotating samples 1, the temperature difference between
the upper and the lower areas of the sample can be reduced with the
aid of the temperature-control device according to the invention,
as compared to the conventional device, by the tenth power, to
values near zero. The use of rotating samples is however standard,
especially in NMR spectroscopy.
The reference numerals in the claims are not meant to restrict the
invention, but are intended to facilitate its understanding.
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